如何对linux中的文件执行按位操作？

Question

我想在Linux上的文件上做一些按位操作(例如xor两个文件),我不知道如何做到这一点.是否有任何命令？

任何帮助将不胜感激.

Answer 1

您可以使用mmap映射文件,对映射的内存应用按位操作,然后将其关闭.

或者,将块读取到缓冲区中,对缓冲区应用操作,并写出缓冲区也可以.

这是一个例子(C,而不是C++;因为除错误处理之外的所有内容都是相同的)反转所有位:

#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/mman.h>
int main(int argc, char* argv[]) {
    if (argc != 2) {printf("Usage: %s file\n", argv[0]); exit(1);}

    int fd = open(argv[1], O_RDWR);
    if (fd == -1) {perror("Error opening file for writing"); exit(2);}

    struct stat st;
    if (fstat(fd, &st) == -1) {perror("Can't determine file size"); exit(3);}

    char* file = mmap(NULL, st.st_size, PROT_READ | PROT_WRITE,
                      MAP_SHARED, fd, 0);
    if (file == MAP_FAILED) {
        perror("Can't map file");
        exit(4);
    }

    for (ssize_t i = 0;i < st.st_size;i++) {
        /* Binary operation goes here.
        If speed is an issue, you may want to do it on a 32 or 64 bit value at
        once, and handle any remaining bytes in special code. */
        file[i] = ~file[i];
    }

    munmap(file, st.st_size);
    close(fd);
    return 0;
}